1. Technical Field
The present invention relates to a light source control device, a projector, and a light source control method.
2. Related Art
Solid-state light sources such as laser diodes (LD) or light emitting diodes (LED) have advantages such as low power consumption, long life, small amount of heat generation, possibility of downsizing, and easiness of lighting/extinction control. Therefore, in recent years, the solid-state light sources have been fast becoming to be used in a variety of fields. For example, in the projectors for displaying images on the screen, the solid-state light sources have started to be actively used for the purpose mainly of reducing the power consumption and the amount of heat generation to thereby achieve downsizing and weight reduction.
The pulse width modulation (PWM) control is often used for controlling the solid-state light sources. This is adopted for the reasons, for example, that the control is easily performed using a digital circuit, that constant light intensity can stably be obtained, and that it is highly efficient. The solid-state light sources used in the projectors are PWM-controlled at a control frequency of about several hundred Hz so as to prevent the flicker from being visually recognized by the user. Further, the light modulation device (e.g., a light valve for modulating the light from the solid-state light source in accordance with an image signal) provided to the projector is also driven at a frequency (e.g., 60 Hz) at which the flicker is not visually recognized by the user.
The flicker caused by performing the PWM control of the solid-state light source and the flicker caused by driving the light modulation device described above are both composed mainly of the high-frequency component which the user fails to recognize visually. However, in some cases, the both flickers interfere with each other to thereby generate a low-frequency component, and thus the flicker and a scroll noise, which can be visually recognized by the user, may be generated. Here, the scroll noise denotes the phenomenon that a stripe-shaped bright part and a stripe-shaped dark part extending in the lateral direction of the screen move slowly upward or downward on the screen. JP-A-2009-175627 (Document 1) discloses a technology of varying the blinking period of the solid-state light source to thereby prevent the scroll noise from occurring.
Incidentally, the technology disclosed in Document 1 mentioned above is for eliminating the regularity of the interference component between the both flickers (the flicker caused by performing the PWM control of the solid-state light source and the flicker caused by driving the light modulation device) by varying the blinking period of the solid-state light source to thereby prevent the scroll noise from occurring. Therefore, the blinking period (the control frequency of the PWM control) of the solid-state light source set in Document 1 is closely associated with the state of the flicker caused by driving the light modulation device.
Therefore, even if the blinking period of the solid-state light source with which the scroll noise can be prevented from occurring for a certain light modulation device is set, there can arise a situation in which the scroll noise cannot be prevented from occurring if the light modulation device changes. Therefore, in the technology disclosed in Document 1 mentioned above, there arises a problem that it is required to reconfigure the blinking period of the solid-state light source, which forces troublesome operations, if the light modulation devices different in characteristics from each other are used.